What's the most important lesson your father have taught you?

When you borrow money from someone, it is a big help. Do not ever think that just because you pay it, it is not. You would not have done what you needed to do without that money. And when you pay back the money lent to you, add extra, no matter how small the amount is coz they could have done something with the money, but instead took a gamble and lent it to you.